Antibodies and kits for immunodetection of epitope tags

ABSTRACT

The instant invention provides antibodies which recognize new epitope tags. Related kits for detecting these epitope tags or fusion proteins having these epitope tags are also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.13/076,678 filed on Mar. 31, 2011, which application is a Divisional ofU.S. patent application Ser. No. 11/974,384 filed on Oct. 12, 2007, thedisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to methods, systems and reagents for improvedimmunodetection of expressed recombinant proteins. Specifically thisinvention relates to the generation of new epitope tags and to thegeneration of novel antibodies against these epitope tags in addition toalready existing epitope tags.

BACKGROUND OF THE INVENTION

Epitope tagging has become an important tool for detecting, localizingand purifying expressed recombinant proteins (Nygren et al., TrendsBiotechnol. 12: 184-188 (1994)). This methodology involves the fusion ofthe tag amino acid sequence to the amino or carboxy terminus of aprotein of interest, and then identifying the tag with a monoclonalantibody (mAb). For most biochemical applications, the use of epitopetags eliminates the need to generate an antibody to the specific proteinthat is to be detected and/or purified.

Currently, there are several validated mAb epitopes in wide use forprotein tagging, including the FLAG peptide epitope (8 amino acidresidues reactive to mAbs M1 and M2) (Hopp et al., BioTechnology 6:1204-1210 (1988)), the V5 epitope (14 amino acids found in the P and Vproteins of paramyxovirus, Simian Virus 5) (Southern et al., J GenVirol. 72: 1551-1557 (1991)), the myc epitope (10 amino acids derivedfrom the c-myc proto-oncogen product) (Evan et al., Mol. Cell. Biol. 5:3610-3616 (1985)), the HA epitope (9 amino acids from the hemagglutininof influenza virus) (Wilson et al., Cell 37(3):7 67-778 (1984)), and the6× His epitope (Lindner et al., BioTechniques 22(1): 140-149 (1997)).

However, the choice of an epitope tag depends on the application,because not all tags and in particular the corresponding mAbs areequally suitable for all immunodetection methods, e.g. Western blotting,immunofluorescence staining, immunoprecipitation, and flow cytometry.Accordingly, there is a need in the art for novel detection tags and theantibodies recognizing those detection tags.

SUMMARY OF THE INVENTION

Accordingly, the present invention fulfills this need by providing inone aspect epitope tags and antibodies against these tags. These epitopetags may comprise an amino acid sequence of SEQ ID NO: 1(SGFANELGPRLMGK). A nucleic acid molecule is also provided wherein thenucleic acid molecule encodes the amino acid SEQ ID NO: 1. In oneembodiment, the nucleic acid sequence is identical to SEQ ID NO: 2.

The antibodies selectively bind SEQ ID NO: 1. In addition, antibodiesthat selectively bind SEQ ID NO: 3 are also provided. Compared toalready existing antibodies, the antibodies described herein exhibit anincreased affinity to epitope tags comprising SEQ ID NO: 1 and SEQ IDNO: 3. In some embodiments, the antibodies are rat IgG monoclonalantibodies (mAb).

In another aspect, fusion proteins and methods for making these proteinsare provided. The fusion proteins comprise an epitope tag comprising anamino acid sequence SEQ ID NO: 1 and an amino acid sequence of a targetprotein.

In yet another aspect, a method of making a fusion protein comprisingSEQ ID NO: 1, and a target protein is provided. The method comprisesintroducing into a host cell a nucleic acid sequence comprising a firstpart encoding SEQ ID NO: 1, and a second part encoding the amino acidsequence for the target protein; culturing the host cell underconditions whereby the fusion protein is expressed; isolating the fusionprotein by binding the fusion protein to an antibody that binds SEQ IDNO: 1 or SEQ ID NO: 2.

In yet another aspect, kits for diagnostic assays for detecting andanalyzing fusion proteins comprising SEQ ID NO: 1, or SEQ ID NO: 3 areprovided. These kits may comprise an antibody that binds to SEQ ID NO:1, or SEQ ID NO: 3, detection means such as another antibody, and,optionally a label.

In another aspect, a cloning vector comprising a nucleic acid sequenceencoding SEQ ID NO: 1 is provided. In some embodiment, the nucleic acidsequence comprises SEQ ID NO: 2. The cloning vector may be provided as akit. Preferably, the kit may also include a OLLAS-tagged control proteinconstruct DNAs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A presents a schematic view of different forms of recombinantmouse Langerin (mLangerin) proteins. Newly generated rat IgG monoclonalantibodies (mAbs) recognize tags expressed as fusions with mLangerin.(1) Schematic view of different forms of recombinant mLangerin proteins.Cytosol, transmembrane (TM) and extracellular domain (ECD) of themLangerin open reading frame (ORF) are indicated. A FLAG epitope tagand/or an E. coli OmpF derived flexible linker (OFL) sequences werefused to the N-terminus of the mLangerin ECD. (3-5) Different mLangerinconstructs cloned into a CMV mammalian expression vector (2) weretransfected into 293T cells, followed by the Western blot analyses withnewly generated rat IgG mAbs, i.e. L31 specific for the mLangerin ECD,and the new L2 and L5 MAbs specific for the sequence tags, and anti-FLAG(M2; mouse IgG mAb from Sigma-Aldrich) and anti-beta-actin.

FIG. 1B illustrates results of the Western blot analyses of constructsof FIG. 1A with newly generated rat antibodies.

FIGS. 2A, 2B and 2C present results of comparison of binding sensitivityto FLAG epitope tagged proteins between mouse mAb M2 and the new rat mAbL5 under similar conditions. (2A) Purified protein comprised ofmLangerin ECD with an N-terminal FLAG tag (structure shown in upperpanel) was diluted as indicated and separated in SDS-PAGE gels followedby blotting with 1 μg/ml of mouse anti-FLAG mAb M2 (middle panel) andrat anti-FLAG mAb L5 (lower panel). (2B) 293T cells were transfectedwith pCMV-FLAG-mSIGN-R1.ECD (structure shown in upper panel), lysed,diluted as indicated, and separated in SDS-PAGE gels followed byblotting with 0.5 μg/ml of mouse anti-FLAG mAb M2 (middle panel) and ratanti-FLAG mAb L5 (lower panel). (2C) 293T cells were transfected withpIRES.Neo3-rP11-FLAG.HA (structure shown in upper panel), lysed, dilutedas indicated, and separated in SDS-PAGE gels followed by blotting with 1μg/ml of mouse anti-FLAG mAb M2 (middle panel) and rat anti-FLAG mAb L5(lower panel).

FIGS. 3A, 3B, and 3C present results of mapping of the epitope tagOLLAS. The epitope of mAb L2 (renamed OLLA-2) is a fusion sequencebetween OFL and mLangerin ECD. (3A) Schematic view of serial deletionsin hCD8.ECD-OFL-mLangerin.ECD fusion proteins. (3B) The series ofC-terminal deletion constructs in FIG. 3A were transfected into 293Tcells, followed by Western blot analyses with anti-hCD8 (left panel) andmAb OLLA-2 (right panel). (3C) The 14 amino acid sequence, named OLLAS(E. coli OmpF Linker mouse Langerin fusion Sequence, SEQ ID NO: 1),residues from both OFL (SEQ ID NO: 18) and mLangerin ECD (SEQ ID NO: 19)was identified as the epitope recognized by mAb OLLA-2. The 3 amino acidresidues (ELG) in the middle of OLLAS epitope correspond to the junctionsequence from the ligation between DNAs for OFL and mLangerin ECD. The 2Asn (N) residues circled are potential sites for N-glycosylation in OFL.Also shown is the sequence of the fusion protein of OFL and mLangerinECD (SEQ ID NO: 20).

FIGS. 4A, 4B, and 4C present the results of immunodetection of OLLAStagged EGFP proteins. (4A) Schematic view of 4 recombinant EGFP proteinswithout a tag (1) or with OLLAS epitope tag attached to the N-terminus(2), C-terminus (3), or internal site (4). The OT1 peptide, a ligand ofmouse MHC I from ovalbumin, were also present in the N-terminus of EGFPprotein 3. The 53 amino acid full-length cytosolic domain from mouseSIGN-R1 was present at the N-terminus of EGFP protein 4. (4B) Expressionvectors for the 4 different recombinant EGFP proteins were transfectedinto 293T cells. Cell lysates (left) were immunoprecipitated (IP) withmAb OLLA-2 (right). Then, all samples were separated in SDS-PAGE gelsfollowed by blotting with anti-GFP (upper panels) and mAb OLLA-2 (lowerpanels). (4C) Expression vectors for EGFP (1; upper panels) and EGFPwith OLLAS tag at the N-terminus (2; lower panels) were transfected intoCHO cells. CHO cells were visualized with the signals for EGFP andimmunofluorescence staining for OLLA-2. Insets in left panels are shownat 1000 fold magnification in the right.

FIGS. 5A and 5B present the results of comparison binding sensitivity ofmAb OLLA-2 and other anti-epitope tag mAbs. (5A) 293T cells weretransfected with pCMV-FLAG.OLLAS-EGFP (structure shown in upper panel),lysed, diluted as indicated, and separated in SDS-PAGE gels followed byblotting with 0.5 μg/ml of anti-FLAG mAb M2 (second panel), the newanti-FLAG mAb L5 (third panel), and mAb OLLA-2 (lower panel). (5B) 293Tcells were transfected with pCMV-V5-hIgG1Fc-OLLAS (structure shown inupper panel), lysed, diluted as indicated, and separated in SDS-PAGEgels followed by blotting with 1 μg/ml of anti-V5 mAb (Invitrogen;middle panel) and mAb OLLA-2 (lower panel).

FIGS. 6A and 6B illustrate production of murinized anti-mouse DEC205 mAbmNLDC145 expressing the OLLAS tag. (6A) Schematic view of theanti-mDEC205 mAb mNLDC145 engineered so that all rat constant domainsare replaced with mouse IgG1 sequences (left) and OLLAS tagged mAbmNLDC145.OLLAS (right). (6B) Expression vectors for mNLDC145 andmNLDC145.OLLAS were transfected into 293 cells. In 2 days, the culturesupernatants from transiently transfected cells were collected andseparated in SDS-PAGE gels followed by blotting with anti-mouse IgG(upper panel) and mAb OLLA-2 (lower panel).

FIGS. 7A, 7B and 7C present the result of immunodetection of mDEC205antibodies shown in FIGS. 6A and 6B with OLLAS epitope tag.Immunodetection with OLLAS epitope tag. (7A) Expression vectors formNLDC145 and mNLDC145.OLLAS as in FIG. 6 were transfected into 293cells. Stable CHO/mDEC205 cells expressing cell surface mDEC205 wereincubated with the culture supernatants containing mNLDC145 (left panel)or mNLDC145.OLLAS (right panel). Then, the cells were further incubatedwith mAb OLLA-2 followed by PE-conjugated anti-rat IgG prior to flowcytometry. (7B) Stable CHO/mDEC205 cells were immunostained with eithermouse control IgG (left panel), mNLDC145 (middle panel), ormNLDC145.OLLAS (right). Then, the cells were probed with anti-mouse IgG,OLLA-2/anti-rat IgG, and DAPI. (7C) Mouse lymph nodes were immunostainedwith rat control IgG (upper panels), rat IgG mAb NLDC145 (middlepanels), and mNLDC145.OLLAS (lower panels. Then, the tissues werestained with mAb OLLA-2 followed by anti-rat IgG labeled with Alexa488and anti-B220. Insets in left panels are shown at 400 fold magnificationin the right.

FIGS. 8A, 8B and 8C present results of immunodetection of engineeredmAbs with protein fusion by the use of OLLAS epitope tag/linker and mAbOLLA-2. (8A) Schematic view of engineered mAbs fused with ovalbuminwhere OLLAS epitope tag was used as a linker. Murinized IgG isotypecontrol mAb, mIsotype.OLLAS.OVA (left), and anti-mDEC205 mAbmNLDC145.OLLAS.OVA (right) are shown. (8B) CHO/mDEC205 cells wereincubated for 15 min with 2 μg/ml of mAb mNLDC145.OLLAS.OVA (rightpanel) or the corresponding isotype control, mIsotype.OLLAS.OVA (leftpanel). After washing, the cells were incubated with different doses ofAlexa647 labeled OLLA-2 or anti-mouse IgG respectively. The analysis wasperformed by FACS. The data are representative of two experiments. (8C)Mouse lymph nodes were immunostained with rat IgG mAb NLDC145 (leftpanel) and murinized mAb mNLDC145.OLLAS.OVA (right panel). Then, thetissues were stained with Alexa647 labeled anti-rat IgG (left panel) orAlexa647 labeled OLLA-2 (right panel) and anti-B220. Bar scales equal 50μm.

FIG. 9 presents results of a secondary structure (SS) analysis of theamino acid (AA) sequences of OFL (solid box) and OLLAS (dashed box)linkers located in four fusion proteins (from top to bottom, SEQ ID NOs:21-24, respectively). Straight lines in SS represent random coilconformations, cylinders helical conformations, and an arrow extended(sheet) conformation. Note that both OFL and OLLAS sequences coexist inmouse IgG1-OFL-mLangerin.ECD (SEQ ID NO: 22).

DETAILED DESCRIPTION OF THE INVENTION

Monoclonal antibodies against epitope tags are an efficient, convenientand rapid method for detecting recombinant protein expression (Jarvikand Telmer, Annu Rev Genet. 32:601-618 (1998)). If there is no antibodyagainst the protein of interest, adding an epitope tag to this proteinallows for protein detection with an antibody against the epitopesequence. Accordingly, in one aspect, novel epitope tags and antibodiesagainst these tags are disclosed.

As used herein, the term “epitope” or “antigenic determinant” refers toa site on an antigen to which B and/or T cells respond or a site on amolecule against which an antibody will be produced and/or to which anantibody will bind. For example, an epitope can be recognized by anantibody defining the epitope. An epitope can be either a “linearepitope” (where a primary amino acid primary sequence comprises theepitope; typically at least 3 contiguous amino acid residues, and moreusually, at least 5, and up to about 8 to about 10 amino acids in aunique sequence) or a “conformational epitope” (an epitope wherein theprimary, contiguous amino acid sequence is not the sole definingcomponent of the epitope). A conformational epitope may comprise anincreased number of amino acids relative to a linear epitope, as thisconformational epitope recognizes a three-dimensional structure of thepeptide or protein. For example, when a protein molecule folds to form athree dimensional structure, certain amino acids and/or the polypeptidebackbone forming the conformational epitope become juxtaposed enablingthe antibody to recognize the epitope. Methods of determiningconformation of epitopes include but are not limited to, for example,x-ray crystallography, two-dimensional nuclear magnetic resonancespectroscopy and site-directed spin labeling and electron paramagneticresonance spectroscopy. See, for example, Epitope Mapping Protocols inMethods in Molecular Biology, Vol. 66, Glenn E. Morris, Ed. (1996), thedisclosure of which is incorporated in its entirety herein by reference.

In one embodiment, the epitope tag may comprise a 14 amino acid sequencepresented herein as SEQ ID NO: 1: SGFANELGPRLMGK, which may be referredto as OLLAS. This sequence resides in the junction between a highlyflexible domain in E. coli OmpF protein, named OFL (OmpF linker), and amouse Langerin extracellular domain (mLangerin ECD). These epitope tagsare referred to herein as OLLAS (E. coli OmpF Linker and mouse Langerinfusion Sequence epitope.)

Alternatively, the epitope tag may comprise a fragment of SEQ ID NO: 1.Some suitable examples of fragments include, but are not limited to, anamino acid sequence with up to 4 amino acid deletion or changes at theN-terminal of the amino acid of SEQ ID NO: 1 or an amino acid sequencewith up to 2 amino acid deletion or changes at the C-terminal of theamino acid of SEQ ID NO: 1. In different embodiments, the suitablefragment comprises at least one of the following:

SEQ ID NO: 4 NELGPRLM SEQ ID NO: 5 ANELGPRLM SEQ ID NO: 6 FANELGPRLMSEQ ID NO: 7 GFANELGPRLM SEQ ID NO: 8 SGFANELGPRLM SEQ ID NO: 9NELGPRLMG SEQ ID NO: 10 ANELGPRLMG SEQ ID NO: 11 FANELGPRLMGSEQ ID NO: 12 GFANELGPRLMG SEQ ID NO: 13 SGFANELGPRLMG  SEQ ID NO: 14NELGPRLMGK SEQ ID NO: 15 ANELGPRLMGK SEQ ID NO: 16 FANELGPRLMGKSEQ ID NO: 17 GFANELGPRLMGK

In another embodiment, an isolated nucleic acid sequence encoding SEQ IDNO: 1 is provided. One with ordinary skills in the art will undoubtedlyunderstand that different nucleic acid sequences may encode the sameamino acid sequence. One example is presented herein as SEQ ID NO: 2:AGT GGC TTT GCG AAT GAA TTG GGA CCT AGG TTG ATG GGC AAG. Furthermore,isolated nucleic acid sequences encoding fragments of SEQ ID NO: 1 areprovided. Sequences for different fragments can be easily construed byone with ordinary skill in the art.

The epitope tags of the instant invention and the nucleic acid sequencesencoding those epitopes may be obtained by a variety of methods wellknown in the art. Considering short size of these amino- and nucleicacid sequences, one of the most convenient ways to make these moleculesis to order them from suppliers who synthesize short peptides andoligonucleotides. Suitable examples of such companies are Invitrogen,Inc., (Carlsbad Calif.) and The Midland Certified Reagent Company, Inc.(Midland, Tex.).

Antibodies against the OLLAS epitope tags are also provided. Suchantibodies, referred to as OLLA-2, selectively bind to SEQ ID NO: 1 andits fragments.

In some embodiments, these antibodies may exhibit an increased affinityto the OLLAS epitope tags compared to other available antibodies and,thus, may enhance the performance of a variety of immunodetectionmethods, including, but not limited to, Western Blot,immunocytochemistry, immunohistochemistry, flow cytometry, andimmunoprecipitation. It has been shown that, by Western blotting, 1μg/ml of anti-V5 mAB is capable of detecting OLLAS in cell lysates fromabout 1250 cells transfected with SEQ ID NO: 1 and 0.5 μg/ml ofanti-Flag mAB M2 is capable of detecting OLLAS in cell lysates fromabout 15,000 such cells. Accordingly, preferably OLLA-2 may be capableof detecting less than the amount detected by anti-Flag mAB M2 andanti-V5 mAB. More preferably, about 1 μg/ml of OLLA-2 may be capable ofdetecting OLLAS from about 10 cells, and 0.5 μg/ml of OLLA-2 may becapable of detecting OLLAS from about 78 of these cells.

In another embodiment, antibodies against a known epitope, FLAG, areprovided which are herein referred to as the new anti-FLAG L5. The FLAGepitope comprises an 8 amino acid sequence SEQ ID NO: 3: DYKDDDDK.Preferably, new anti-FLAG L5 is capable of binding to SEQ ID NO: 3 withincreased affinity compared to existing antibodies against FLAG, andthus, enhances the performance of a variety of immunodetection methods,including Western Blot, immunocytochemistry, immunohistochemistry, flowcytometry, and immunoprecipitation. In one embodiment, the new anti-FLAGL5 may detect both N-terminal and C-terminal FLAG tagged proteins about2 to 8 times better than the conventional anti-FLAG mAb M2 using theWestern blot analysis. Preferably, in Western blot analysis, 1 mg/ml ofnew anti-FLAG L5 can detect less than 100 ng of N-terminally FLAG taggedpurified protein or lysates from about 2,500 cells transfected withN-terminally FLAG tagged recombinant protein construct, and morepreferably it can detect about as little as 25 ng of N-terminally FLAGtagged purified protein or lysates from about 1,250 cells transfectedwith N-terminally FLAG tagged recombinant protein construct.

OLLA-2 and new anti-FLAG L5 antibodies may take one of many forms knownin the art. The term “antibody” is used here in the broadest sense andspecifically covers monoclonal antibodies (including full lengthmonoclonal antibodies), polyclonal antibodies, monospecific antibodies,multispecific antibodies (e.g., bispecific antibodies), antibodyderivatives, functional equivalents and antibody fragments so long asthey retain its antigen binding capability, generally including, but notlimited to, the specific binding member or antigen-binding portion. Theterms “specific binding member” and “antigen-binding portion” include,but are not limited to, (i) a Fab fragment, a monovalent fragmentconsisting of the VL, VH, CL and CH domains; (ii) a F(ab′)2 fragment, abivalent fragment comprising two Fab fragments linked by a disulfidebridge at the hinge region; (iii) a Fd fragment consisting of the VH andCH domains; (iv) a Fv fragment consisting of the VL and VH domains of asingle arm of an antibody (v) a dAb fragment, which comprises a VHdomain; (vi) an isolated complementarily determining region (CDR); (vii)a ‘scAb’, an antibody fragment containing VH and VL as well as either CLor CH; and (viii) artificial antibodies based upon protein scaffolds,including but not limited to fibronectin type III polypeptide antibodies(e.g., see U.S. Pat. No. 6,703,199, issued to Koide on Mar. 9, 2004 andPCT International Application Publication No. WO 02/32925).

The term “monoclonal antibody” as used herein refers to an antibodyobtained from a population of substantially homogeneous antibodies,i.e., the individual antibodies comprising the population are identicalexcept for possible naturally occurring mutations that may be present inminor amounts. Monoclonal antibodies are highly specific, being directedagainst a single antigenic site. Furthermore, in contrast toconventional (polyclonal) antibody preparations that typically includedifferent antibodies directed against different determinants (epitopes),each monoclonal antibody is directed against a single determinant on theantigen. The modifier “monoclonal” indicates the character of theantibody as being obtained from a substantially homogeneous populationof antibodies, and is not to be construed as requiring production of theantibody by any particular method. Monoclonal antibodies may begenerated from different species, including but not limited to, mice,rats, rabbits, or primates.

For example, the monoclonal antibodies to be used in accordance with themethods disclosed herein may be made by the hybridoma method firstdescribed by Kohler and Milstein, Nature, 256, 495-497 (1975), which isincorporated herein by reference. Alternatively, the monoclonalantibodies may be made by recombinant DNA methods which are disclosed,for example, in U.S. Pat. No. 4,816,567, which is incorporated herein byreference, and are also generally described below. Finally, techniquesare available to the artisan for the selection of antibody fragmentsfrom libraries using enrichment technologies, including but not limitedto phage display, ribosome display (Hanes and Pluckthun, 1997, Proc.Nat. Acad. Sci. 94: 4937-4942), bacterial display (Georgiou, et al.,1997, Nature Biotechnology 15: 29-34) and/or yeast display (Kieke, etal., 1997, Protein Engineering 10: 1303-1310.)

Beyond species specific monoclonal antibodies described above, theantibodies of the present invention may also be in the form of a“chimeric antibody”, a monoclonal antibody constructed from the variableregions derived from say, the murine source, and constant regionsderived from the intended host source (e.g., human; for a review, seeMorrison and Oi, 1989, Advances in Immunology, 44: 65-92). The variablelight and heavy genes from the rodent (e.g., mouse) antibody are clonedinto a mammalian expression vector which contains an appropriate humanlight chain and heavy chain coding region, respectively. These heavy andlight “chimeric” expression vectors are cotransfected into a recipientcell line and selected and expanded by known techniques. This cell linemay then be subjected to known cell culture techniques, resulting inproduction of both the light and heavy chains of a chimeric antibodySuch chimeric antibodies have historically been shown to have theantigen-binding capacity of the original rodent monoclonal whilesignificantly reducing immunogenicity problems upon host administration.

A logical improvement to the chimeric antibody is the “humanizedantibody,” which arguably reduces the chance of the patient mounting animmune response against a therapeutic antibody when compared to use of achimeric or full murine monoclonal antibody The strategy of “humanizing”a murine Mab is based on replacing amino acid residues which differ fromthose in the human sequences by site directed mutagenesis of individualresidues or by grafting of entire complementarily determining regions(Jones et al., 1986, Nature 321: 522-526). This technology is again nowwell known in the art and is represented by numerous strategies toimprove on this technology; namely by implementing strategies including,but not limited to, “reshaping” (see Verhoeyen, et al., 1988, Science239: 1534-1536), “hyperchimerization” (see Queen, et al., 1991, Proc.Natl. Acad. Sci. 88:2869-2873) or “veneering” (Mark, et al., 1994,Derivation of Therapeutically Active Humanized and Veneered anti-CD18Antibodies Metcalf end Dalton, eds. Cellular Adhesion: MolecularDefinition to Therapeutic Potential. New York: Plenum Press, 291-312).These strategies all involve to some degree sequence comparison betweenrodent and human sequences to determine whether specific amino acidsubstitutions from a rodent to human consensus is appropriate. Whateverthe variations, the central theme involved in generating a humanizedantibody relies on CDR grafting, where these three antigen binding sitesfrom both the light and heavy chain are effectively removed from therodent expressing antibody clone and subcloned (or “grafted”) into anexpression vector coding for the framework region of the human antibody.Therefore, a “humanized antibody” is effectively an antibody constructedwith only murine CDRs (minus any additional improvements generated byincorporating one or more of the above mentioned strategies), with theremainder of the variable region and all of the constant region beingderived from a human source.

Yet another improvement over re-engineered antibodies as reviewed aboveis the generation of fully human monoclonal antibodies. The firstinvolves the use of genetically engineered mouse strains which possessan immune system whereby the mouse antibody genes have been inactivatedand in turn replaced with a repertoire of functional human antibodygenes, while leaving other components of the mouse immune systemunchanged. Such genetically engineered mice allow for the natural invivo immune response and affinity maturation process which results inhigh affinity, fully human monoclonal antibodies This technology isagain now well known in the art and is fully detailed in variouspublications, including but not limited to U.S. Pat. Nos. 5,939,598;6,075,181; 6,114,598; 6,150,584 and related family members (assigned toAbgenix, disclosing their XenoMouse technology); as well as U.S. Pat.Nos. 5,545,806; 5,569,825; 5,625,126; 5,633,425; 5,789,650; 5,877, 397;5,661,016; 5,814,318; 5,874,299; and 5,770,429 (assigned to GenPharmInternational and available through Medarex, under the umbrella of the“UltraMab Human Antibody Development System”). See also a review fromKellerman and Green (2002, Curr. Opinion in Biotechnology 13: 593-597).

In the preferred embodiments, the L2 anti-OLLAS antibodies (which mayalso be referred to as OLLA-2 antibodies) and new anti-FLAG L5antibodies are rat monoclonal antibodies.

In another aspect, fusion proteins are provided. In one embodiment, thefusion proteins may comprise epitope tags encoded by SEQ ID NO: 1 or itsfragments (such as SEQ ID NO: 4-SEQ ID NO: 17), and an amino acidsequence of a target protein. The epitope tags may be connected to theC-terminal, the N-terminal or both N- and C-termini of the targetprotein. Furthermore, methods of making such fusion proteins areprovided. The methods comprise introducing into a host cell a nucleicacid sequence comprising a first part encoding the epitope tag, and asecond part encoding an amino acid sequence for the target protein,culturing the host cell under conditions that promote expression ofprotein linked to the epitope tag, and isolating the fusion protein.

The term “isolating” or “isolated” is used herein as it is used withinthe art. It means that antibodies, antibody fragment/specific bindingmembers, nucleic acid molecules, and proteins are free or substantiallyfree of material with which they are naturally associated such as otherpolypeptides or nucleic acids with which they are found in their naturalenvironment, or the environment in which they are prepared (e.g. cellculture) when such preparation is by recombinant DNA technology(practiced ill vitro) or in vivo. “Isolating” or “isolated” covers anyform containing the identified and characterized antibodies, antibodyfragments/specific binding members, nucleic acid molecules, proteinsdescribed herein following their removal from that initial environment.

Techniques for such manipulations are well known and are readilyavailable to the artisan of ordinary skill in the art. Many treatises onrecombinant DNA methods have been published, including Sambrook, et al.,Molecular Cloning: A Laboratory Manual, 2^(nd) edition, Cold SpringHarbor Press, (1988), Davis, et al., Basic Methods in Molecular Biology,Elsevier (1986), and Ausubel, et al., Current Protocols in MolecularBiology, Wiley Interscience (1988). These reference manuals arespecifically incorporated by reference herein in their entirety.

In general, a nucleic acid molecule comprising a sequence encoding anepitope tag and a nucleic acid molecule encoding a target protein may belinked, in whole or in part, to form “recombinant DNA molecules” whichencode a desired fusion protein. These recombinant DNA molecules may beprepared using any known technique. For example, the sequences for theeptiope tag and the target protein may be cloned, sequenced and ligatedto make the recombinant DNA molecule for the fusion protein. In oneembodiment, the sequences may be generated and cloned using thepolymerase chain reaction (PCR). Alternatively, a cloning vectorcomprising of DNA or RNA may be employed. Cloning vectors are definedherein as an agent that can carry and reproduce a DNA fragment into ahost cell. For most cloning purposes DNA vectors are preferred. Typicalvectors include plasmids, modified viruses, bacteriophage, cosmids,yeast artificial chromosomes, and other forms of episomal or integratedDNA. It is within the purview of the skilled artisan to determine anappropriate vector for a particular gene transfer and generation of arecombinant DNA for a fusion protein or other use.

In one aspect, cloning vectors comprising a nucleic acid sequenceencoding SEQ ID NO: 1 are provided. As stated above, cloning vectors aredefined herein as agents that can carry and reproduce a DNA fragmentinto a host cell. In one exemplary embodiment, the nucleic acid sequencemay comprise SEQ ID NO: 2. The cloning vector may be prepared by anyknown technique such as described in reference manuals cited above. Thecloning vector may further include a polyadenylation signal, atranscription termination sequence, and a multiple cloning sitecomprising at least one endonuclease restriction site. The vector mayfurther comprise a promoter. In some embodiments, in the operationalvector, the nucleic acid sequence may be located upstream of thepolyadenylation signal and the transcription termination sequence, andthe at least one endonuclease restriction site may be located upstreamof said polyadenylation signal and the transcription terminationsequence.

A target nucleic acid sequence may be cloned into the multiple cloningsite of the cloning vector. It is preferable that the nucleic acidsequence encoding SEQ ID NO: 1 or its fragments, and the target nucleicacid sequence may be transcribed as a single mRNA and translated into asingle amino acid sequence that includes SEQ ID NO: 1 or its fragments.Depending on the desired location of the epitope tag in the fusionprotein, the at least one endonuclease restriction site may be locateddownstream of the nucleic acid sequence encoding SEQ ID NO: 1 or itsfragments for N-terminal tagging, or upstream of the nucleic acidsequence encoding SEQ ID NO: 1 or its fragments for C-terminal tagging,or both.

The cloning vector may be provided as a kit. In addition to the cloningvector, the kit may include a forward primer; a reverse primer; aligase; at least one restriction endonuclease; an aliquote of competentcells; instructions or any combinations thereof. The kit may alsoinclude a control. In one exemplary embodiment, the control may be avector comprising a DNA sequence that encodes a known OLLAS-taggedprotein (e.g., a GFP protein).

Once recombinant DNA molecules are prepared, they may be inserted intoan expression vector and transfected into a host cell. Methods ofsubcloning nucleic acid molecules of interest into expression vectors,transforming or transfecting host cells containing the vectors, andmethods of making substantially pure protein comprising the steps ofintroducing the respective expression vector into a host cell, andcultivating the host cell under appropriate conditions are well known.The fusion protein so produced may be harvested from the host cells inconventional ways. Any known expression vector may be utilized topractice this portion of the invention, including any vector containinga suitable promoter and other appropriate transcription regulatoryelements. The resulting expression construct is transferred into aprokaryotic or eukaryotic host cell to produce recombinant protein.

Expression vectors are defined herein as DNA sequences that are requiredfor the transcription of cloned DNA and the translation of their mRNAsin an appropriate host. Such vectors can be used to express eukaryoticDNA in a variety of hosts such as bacteria, blue green algae, plantcells, insect cells and animal cells. Specifically designed vectorsallow the shuttling of DNA between hosts such as bacteria-yeast orbacteria-animal cells. An appropriately constructed expression vectorshould contain: an origin of replication for autonomous replication inhost cells, selectable markers, a limited number of useful restrictionenzyme sites, a potential for high copy number, and active promoters. Apromoter is defined as a DNA sequence that directs RNA polymerase tobind to DNA and initiate RNA synthesis. A strong promoter is one whichcauses mRNAs to be initiated at high frequency.

Commercially available mammalian expression vectors which may besuitable, include but are not limited to, pcDNA3.neo (Invitrogen),pcDNA3.1 (Invitrogen), pCI-neo (Promega), pLITMUS28, pLITMUS29,pLITMUS38 and pLITMUS39 (New England Bioloabs), pcDNAI, pcDNAIanp(Invitrogen), pcDNA3 (Invitrogen), pMClneo (Stratagene), pXT1(Stratagene), pSG5 (Stratagene), EBO pSV2-neo (ATCC 37593) pBPV-1(8-2)(ATCC 37110), pdBPV-MMTneo(342-12) (ATCC 37224), pRSVgpt (ATCC 37199),pRSVneo (ATCC 37198), pSV2-dhfr (ATCC 37146), pUCTag (ATCC 37460), and1ZD35 (ATCC 37565). Also, a variety of bacterial expression vectors areavailable, including but not limited to pCR2.1 (Invitrogen), pET1 la(Novagen), lambda gtl 1 (Invitrogen), and pKK223-3 (Pharmacia). Inaddition, a variety of fungal cell expression vectors may be used,including but not limited to pYES2 (Invitrogen) and Pichie expressionvector (Invitrogen). Also, a variety of insect cell expression vectorsmay be used, including but are not limited to pBlueBacIII andpBlueBacHis2 (Invitrogen), and pAcG2T (Pharmingen).

Recombinant host cells may be prokaryotic or eukaryotic, including butnot limited to, bacteria such as E. coli, fungal cells such as yeast,mammalian cells including, but not limited to, cell lines of bovine,porcine, monkey and rodent origin; and insect cells. Mammalian specieswhich may be suitable, include but are not limited to, L cells L-M(TK−)(ATCCCCL1.3), L cells L-M (ATCC CCL 1.2), Saos-2 (ATCCHTB-85), 293(ATCCCRL1573), Raji (ATCC CCL 86), CV-1 (ATCC CCL 70), COS-1 (ATCCCRL1650), COS-7(ATCC CRL 1651), CHO-K1 (ATCC CCL 61), 3T3 (ATCC CCL 92),NIH/3T3 (ATCC CRL 1658), HeLa (ATCC CCL 2), C1271 (ATCC CRL 1616),BS-C-1(ATCC CCL 26), MRC-5 (ATCCCCL171) and CPAE (ATCC CCL 209).

The fusion proteins of interest may be isolated using any known proteinpurification technique. Suitable examples include, but are not limitedto, immuno-affinity chromatography, affinity chromatography, proteinprecipitation, buffer exchange, ion exchange chromatography, hydrophobicinteraction chromatography, size-exclusion chromatography,electrophoresis or combination thereof. In the preferred embodiment, thefusion protein is isolated using the OLLA-2 or new anti-FLAG L5antibodies. These antibodies may be dissociated from the fusion proteinusing any known techniques such as by cleaving the antibody off using aprotease or washing the antibody-antigen complex with a solution whichfavors dissociation of the antigen and the antibody (for example, usingthe solution of high ionic strength). Many of these techniques aredescribed, for example, in Biochemistry, R. H. Garrett and C. M.Grisham, Suanders College Publishing, (1995); and Molecular and CellBiology, Third Edition, H Lodish, D. Baltimore, A. Berk, S. L. Zipursky,P. Matsudaira, J. Darnell, Scientific American Books, Inc. (1995), whichare incorporated herein by reference.

In yet another aspect, kits for diagnostic assays for detecting andanalyzing tagged protein are provided. Such assays may be carried out byany techniques known and available to the artisan, including but notlimited to Western blots, ELISAs, radioimmunoassays, immunohistochemicalassays, immunoprecipitations, or other immunochemical assays known inthe art. These kits may comprise any of the antibodies described above,detection means corresponding to the antibody, and, optionally a label.

The antibodies described herein may be used as the basic reagents in anumber of different immunoassays to determine the presence of a proteintagged either with OLLAS or FLAG epitopes in a sample. Generallyspeaking, the antibodies can be employed in any type of immunoassay,whether qualitative or quantitative. This includes both the two-sitesandwich assay and the single site immunoassay of the non-competitivetype, as well as in traditional competitive binding assays.

One embodiment of interest, for ease of detection, and its quantitativenature, is the sandwich or double antibody assay, of which a number ofvariations exist, all of which are intended to be encompassed by thisportion of the present invention. For example, in a typical forwardsandwich assay, unlabeled antibody is immobilized on a solid substrate,e.g., microtiter plate wells, and the sample to be tested is broughtinto contact with the bound molecule. After a suitable period ofincubation, for a period of time sufficient to allow formation of anantibody-antigen binary complex, a second antibody, labeled with areporter molecule capable of inducing a detectable signal, is then addedand incubation is continued allowing sufficient time for binding withthe antigen at a different site and the formation of a ternary complexof antibody-antigen-labeled antibody. Any unreacted material is washedaway, and the presence of the antigen is determined by observation of asignal, which may be quantitated by comparison with a control samplecontaining known amounts of antigen.

Variations on the forward sandwich assay include the simultaneous assay,in which both sample and antibody are added simultaneously to the boundantibody, or a reverse sandwich assay in which the labeled antibody andsample to be tested are first combined, incubated and added to theunlabelled surface bound antibody. These techniques are well known tothose skilled in the art, and the possibility of minor variations willbe readily apparent. As used herein, “sandwich assay” is intended toencompass all variations on the basic two-site technique.

For the sandwich assays, the only limiting factor is that bothantibodies have different binding specificities for the OLLAS or FLAGepitopes. Thus, a number of possible combinations are possible. As amore specific example, in a typical forward sandwich assay, a primaryantibody is either covalently or passively bound to a solid support. Thesolid surface is usually glass or a polymer, the most commonly usedpolymers being cellulose, polyacrylamide, nylon, polystyrene,polyvinylchloride or polypropylene. The solid supports may be in theform of tubes, beads, discs or microplates, or any other surfacessuitable for conducting an immunoassay. The binding processes are wellknown in the art. Following binding, the solid phase-antibody complex iswashed in preparation for the test sample. An aliquot of the samplecontaining a protein tagged with either OLLAS or FLAG epitope to betested is then added to the solid phase complex and incubated at 25° C.for a period of time sufficient to allow binding of any tagged proteinspresent to the antibody specific for that tag. The second antibody isthen added to the solid phase complex and incubated at 25° C. for anadditional period of time sufficient to allow the second antibody tobind to the primary antibody-antigen solid phase complex. The secondantibody may be linked to a reporter molecule, the visible signal ofwhich is used to indicate the binding of the second antibody to anyantigen in the sample. By “reporter molecule”, as used in the presentspecification is meant a molecule which by its chemical nature, providesan analytically detectable signal which allows the detection ofantigen-bound antibody. Detection must be at least relativelyquantifiable, to allow determination of the amount of antigen in thesample, this may be calculated in absolute terms, or may be done incomparison with a standard (or series of standards) containing a knownnormal level of antigen.

The most commonly used reporter molecules in this type of assay areeither enzymes or fluorophores. In the case of an enzyme immunoassay anenzyme is conjugated to the second antibody, often by means ofglutaraldehyde or periodate. As will be readily recognized, however, awide variety of different conjugation techniques exist, which are wellknown to the skilled artisan. Commonly used enzymes include horseradishperoxidase, glucose oxidase, beta-galactosidase and alkalinephosphatase, among others. The substrates to be used with the specificenzymes are generally chosen for the production, upon hydrolysis by thecorresponding enzyme, of a detectable color change. For example,p-nitrophenyl phosphate is suitable for use with alkaline phosphataseconjugates; for peroxidase conjugates, 1,2-phenylenediamine or toluidineare commonly used. It is also possible to employ fluorogenic substrates,which yield a fluorescent product rather than the chromogenic substratesnoted above. In all cases, the enzyme-labeled antibody is added to thefirst antibody-antigen complex and allowed to bind to the complex, andthen the excess reagent is washed away. A solution containing theappropriate substrate is then added to the tertiary complex ofantibody-antigen-labeled antibody. The substrate reacts with the enzymelinked to the second antibody, giving a qualitative visual signal, whichmay be further quantitated, usually spectrophotometrically, to give anevaluation of the amount of antigen that is present in the serum sample.

Additionally, fluorescent compounds, such as fluorescein or rhodamine,may be chemically coupled to antibodies without altering their bindingcapacity. When activated by illumination with light of a particularwavelength, the fluorochrome-labeled antibody absorbs the light energy,inducing a state of excitability in the molecule, followed by emissionof the light at a characteristic longer wavelength. The emission appearsas a characteristic color visually detectable with a light microscope.As in the enzyme immunoassay (EIA), the fluorescent-labeled antibody isallowed to bind to the first antibody-tagged protein complex. Afterwashing the unbound reagent, the remaining ternary complex is thenexposed to light of the appropriate wavelength, and the fluorescenceobserved indicates the presence of the antigen. Immunofluorescence andEIA techniques are both very well established in the art and areparticularly preferred for the present method. However, other reportermolecules, such as radioisotopes, chemiluminescent or bioluminescentmolecules may also be employed. It will be readily apparent to theskilled artisan how to vary the procedure to suit the required use.

In another embodiment, the sample to be tested may be used in a singlesite immunoassay wherein it is adhered to a solid substrate eithercovalently or noncovalently. An unlabeled anti-OLLAS or anti-FLAGantibody is brought into contact with the sample bound on the solidsubstrate. After a suitable period of incubation, for a period of timesufficient to allow formation of an antibody-antigen binary complex asecond antibody, labeled with a reporter molecule capable of inducing adetectable signal, is then added and incubation is continued allowingsufficient time for the formation of a ternary complex ofantigen-antibody-labeled antibody. For the single site immunoassay, thesecond antibody may be a general antibody (i.e., zenogeneic antibody toimmunoglobulin, particularly anti-(IgM and IgG) linked to a reportermolecule) that is capable of binding an antibody that is specific forthe tagged protein of interest.

Commercially available, conventional anti-tag mAbs are mostly, if notall, made from mouse. The mouse anti-tag mAbs are not readily usable forthe studies on mouse tissues or in vivo applications in mouse, unlessthey are directly labeled with fluorochromes, enzymes, or otherdetectable means, which would make those materials rare and costly.Therefore, the new anti-OLLAS tag mAb OLLA-2 from rat IgG will providean extra advantage over conventional mouse anti-tag mAbs, as theinventors have illustrated that mAb OLLA-2 can be used directly in mousein vivo and detected in mouse tissues without special, direct labelings.

Selected embodiments will not be further discussed in the followingexample. The example is illustrative only, and is not intended to limitthe instant disclosure in any way.

EXAMPLES Materials and Methods

Production of Epitope Specific MAb hybridoma.

Animals and cell lines: Wistar Furth rats were purchased from CharlesRiver Laboratories (Wilmington, Mass.). C57BL/6 and BALB/c mice werepurchased from Taconic Farms (Hudson, N.Y.) and Charles River Labs, andused at 6-8 wks of age. All animals were maintained under specificpathogen-free conditions. Animal care and experiments were conductedaccording to institutional guidelines of the Rockefeller University andMemorial Sloan-Kettering Cancer Center.

Chinese hamster ovary (CHO) cells and 293T cells were cultured in DMEMwith 7% FBS or 5% Ultra-Low IgG FBS supplemented with 2mM glutamine(Gibco BRL, Invitrogen, Carlsbad, Calif.), antibiotics (Invitrogen) andnon-essential amino acids (Invitrogen).

MAb hybridoma production: Generation and screening of mAb hybridomasagainst FLAG/OFL tagged mLangerin ECD were described previously (Cheonget al., J Immunol Methods. 2007 324(1-2):4842 (2007)). In brief, WistarFurth rats were immunized with the purified proteins of mLangerin ECDfused with OFL and human IgG1 Fc (GenBank accession no. DQ917567, SEQ IDNO: 25) and FLAG/OFL tagged mLangerin ECD (GenBank accession no.DQ917568, SEQ ID NO: 26), followed by the injection of mouse dendriticcells enriched from ear skin organ cultures (Cheong et al., 2007). Then,the cells from spleen were used for hybridoma fusion at the MonoclonalAntibody Core Facility of the Rockefeller University and Memorial SloanKettering Cancer Center. Culture supernatants from the hybridomas werescreened on ELISA with FLAG/OFL tagged mLangerin ECD protein aspreviously described (Cheong et al., 2007).

Reagents: To purify mAbs L2, L5, L31 and NLDC145, the supernatants ofindividual hybridomas were cultured and the mAbs were purified withprotein G (Pierce, Rockford, Ill.; GE Healthcare, Piscataway, N.J.)column, according to the manufacture's instructions. The followingreagents were purchased; ANTI-FLAG® M2, DAPI (Sigma-Aldrich, St. Louis,Mo.), anti-beta actin (Abcam Inc., Cambridge, Mass.), anti-human CD8(Santa Cruz Biotechnology, Inc., Santa Cruz, Calif.), pEGFP-N1, anti-GFP(Clontech, Mountain View, Calif.), anti-B220 (BD Biosciences, San Jose,Calif.), anti-V5 (Invitrogen), HRP-conjugated anti-mouse IgG and HRP- orPE-conjugated anti-rat IgG (Southern Biotech, Birmingham, Ala.),PE-conjugated anti-mouse IgG (Jackson ImmunoResearch Laboratories, Inc.,West Grove, Pa.), Alexa350-, Alexa488- or Alexa647-conjugated anti-ratIgG and Alexa647-conjugated anti-mouse IgG (Molecular Probes,Invitrogen).

Vector constructions and expression of recombinant proteins: Theconstruction, expression and purification of murinized heavy and lightchains for anti-DEC205 mAb NLDC145 (mNLDC145) and isotype control mAbhave been described (Hawiger et al., J Exp Med. 194(6):769-779 (2001)).The sequences of OLLAS peptide (SGFANELGPRLMGK/SEQ ID NO: 1; GenBankaccession no. EF635496, SEQ ID NO: 27) or OLLAS-tagged ovalbumin(GenBank accession no. EF635488, SEQ ID NO: 28) were inserted at thecarboxy-terminus in heavy chains of mNLDC145 or isotype control mAbs.293T cells were transfected with the expression vectors for mNLDC145 orisotype control mAbs carrying OLLAS-tagged inserts. Then, the culturesupernatants or mAbs purified by Protein G affinity column were used forfurther analyses. Soluble FLAG-mLangerin.ECD protein was purified fromculture supernatants of the stable CHO/FLAG-mLangerin.ECD cells byANTI-FLAG® M1 Affinity Gel (Sigma-Aldrich) following the manufacturer'sinstruction.

The generation of expression vectors for the open reading frames (ORFs)of full-length mLangerin and soluble fusion mLangerin ECD with FLAG/OFLwas described previously (Cheong et al., 2007). The cDNAs for epitopetags or subdomains of individual genes were generated by PCR, sequenced,and ligated to make the ORFs for respective recombinant fusion proteins.Then, the ORFs were cloned into pCMV mammalian expression vector(Clontech) and stably transfected into CHO cells or transientlytransfected to 293T cells. The expression vectors for the ORFs offollowing recombinant proteins were generated; FLAG-mLangerin.ECD(GenBank accession no. EF635489, SEQ ID NO: 29),FLAG-OFL/2-mLangerin.ECD (GenBank accession no. EF635490, SEQ ID NO:30), FLAG-mSIGN-R1.ECD (GenBank accession no. EF635491, SEQ ID NO: 31),rat P11-FLAG.HA (GenBank accession no. EF635492, SEQ ID NO: 32), humanCD8.ECD-OFL-mLangerin.ECD (GenBank accession no. EF635493, SEQ ID NO:33), hCD8.ECD-OFL-mLangerin.ECD.deletion.#1 (GenBank accession no.EF635494, SEQ ID NO: 34), hCD8.ECD-OFL-mLangerin.ECD.deletion.#2(GenBank accession no. EF635495, SEQ ID NO: 35), OT1-EGFP-OLLAS (GenBankaccession no. EF635497, SEQ ID NO: 36), FLAG.OLLAS-EGFP (GenBankaccession no. EF635498, SEQ ID NO: 37). V5-hIgG1Fc-OLLAS was generatedfrom V5-hIgG1Fc-OFL-mLangerin.ECD (GenBank accession no. DQ917567, SEQID NO: 25; Cheong et al., 2007) by replacing OFL-mLangerin.ECD withOLLAS. OLLAS-EGFP and mSIGN-R1.Cytosol-OLLAS-EGFP were generated byinserting OLLAS or mSIGN-R1.Cytosol-OLLAS (GenBank accession no.EF635499, SEQ ID NO: 38) sequences into the multi-cloning site ofpEGFP-N1 vector (Clontech).

Characterization of mAbs.

SDS-PAGE and Western blot analysis: 293T cells were transfected with theexpression vectors for recombinant fusion proteins, harvested at day 2,lysed in RIPA buffer (150 mM NaCl, mM Tris-HCl, pH 8.0, 1% NonidentP-40, 0.5% sodium deoxycholate and 0.1% SDS) supplemented with proteaseinhibitor cocktails (Sigma-Aldrich), and stored at −20° C. Each lysedsample was mixed with an equal volume of 2×SDS PAGE sample buffer andboiled at 95° C. for 5 min. Then the samples were separated in 12 or 15%SDS-PAGE and transferred onto PVDF membranes, followed by incubationwith antibodies. Antibody-reactive bands on the blots were visualized byincubation with peroxidase-labeled secondary Ab followed by treatmentwith ECL Plus™ reagents (GE Healthcare). The isotypes of mAb heavy andlight chains were determined by the Western blot analysis using mAbsupernatant as primary Ab and rat isotype specific HRP-conjugated Abs(Southern Biotech) as secondary Ab.

Immunofluorescence: Stably transfected CHO cells and lymph nodessections were examined for immunofluorescence as described previously.(Kang et al, Int Immunol. (2):177-86 (2003); Kang et al, Proc Natl AcadSci USA. 101(1):215-220(2004)). Cells cultured on slides were washedwith PBS, fixed in acetone for 5 min, and subsequently washed andblocked with PBS with 3% BSA for 1 hr. Then, after incubation withprimary Abs for 1 hr at room temperature, cells were washed andincubated with fluorochrome-labeled secondary Abs. For tissue staining,peripheral lymph nodes from C57BL/6 mice were collected and embedded inTissue-Tek OCT® (optimal cutting temperature) compounds (Sakura FinetekUSA, Torrance, Calif.) before freezing at −80° C. Frozen tissues weresectioned 10 μm in thickness on a microtome and fixed in cold acetonefor 15 min. Sections were incubated with primary Abs at room temperaturein a humidified chamber for 1 hr, washed and then incubated withfluorochrome-labeled secondary Abs. Sections were mounted in Aqua-PolyMount (Polysciences, Warrington, Pa.) and were stored at 4° C. untilmicroscopic examination. The images were acquired with a deconvolutionmicroscopy (Olympus, Melville, N.Y.) or with a Zeiss LSM 510 system(Carl Zeiss MicroImaging, Thornwood, N.Y.) at the Rockefeller UniversityBio-Imaging Resource Center.

FACS analysis: After detaching with 1 mM EDTA in PBS for 10 min,CHO/mDEC205 cells were incubated with primary Abs for 15 min at 4° C.Cells were washed, detected by Alexa 647 conjugated secondary Abs for 15min at 4° C., and analyzed with FACSCalibur flow cytometer (BDBiosciences) at the Rockefeller University Flow Cytometry ResourceCenter.

Sequence analysis: The sequences of OFL and OLLAS were analyzed byPSIPRED (Bryson et al., Nucleic Acids Res. 33(Web Server issue), W36.(2005); McGuffin et al., Bioinformatics 16(4):404-405 (2000)) using thePSIPRED Protein Structure Prediction Server, and the NCBI BLAST databasewere searched for the sequence similarities.

Example 1 MAb L5 Recognizes the FLAG Epitope and L2 Recognizes an OFLDependent Tag

To identify the epitopes of newly generated rat IgG mAbs L2 and L5, theinventors first made different forms of recombinant mLangerin proteinswith/without E. coli OmpF derived flexible linker (OFL) sequences (FIG.1A), which consisted of 17 amino acid residues, NATPITNKFTNTSGFAN (SEQID NO: 18). FLAG epitope tags with full or half-deleted OFL or withoutOFL were fused to the N-terminus of mLangerin extracellular domain (ECD)for which a specific L31 mAb was recently obtained and described (Cheonget al., 2007). These constructs were cloned into CMV mammalianexpression vectors and transfected to 293T cells. The cell lysates weresubjected to Western blot analyses (FIG. 1B), using mAbs L2 and L5 incomparison with L31 (anti-mLangerin; Cheong et al., 2007) and thecommercial mAb M2 (ANTI-FLAG® from Sigma Aldrich). The results indicatedthat, while anti-mLangerin mAb L31 recognized all the recombinantproteins containing mLangerin ECD, mAb L2 only detected the tworecombinant proteins containing OFL sequences (FIG. 1B, lanes 3 & 4).Since constructs containing mLangerin ORF (FIG. 1B, lane 1) or FLAG only(FIG. 1B, lane 5) were not detected by mAb L2, the epitope of mAb L2 isdifferent from the epitopes identified by anti-mLangerin L31 andanti-FLAG M2. Interestingly, mAb L2 could detect the constructcontaining half-deleted OFL sequence (FIG. 1B, lane 4) where twoN-glycosylation sites in OFL were removed (FIG. 3C) and where twoN-terminal amino acids were absent from the OLLAS epitope of SEQ ID NO:1 (See FIG. 1B, lane 4).

Another newly generated mAb L5 was specifically reactive to all therecombinant proteins containing a FLAG sequence, but not mouse Langerinitself, similarly to anti-FLAG mAb M2 (FIG. 1B). Thus, mAb L5 is a newrat IgG mAb against the FLAG epitope. The inventors also have used mAbL5 efficiently in the immunoprecipitation and immunofluorescentdetection of FLAG tagged recombinant proteins (data not shown).

Example 2 Comparison of Anti-FLAG Binding Sensitivity Between Rat IgGmAb L5 and a Commercially Available Mouse IgG mAb M2

To compare the binding sensitivity to the FLAG epitope between mouse IgGmAb M2 and the new rat IgG mAb L5, the inventors performed Western blotanalyses with different FLAG tagged proteins. First, the purifiedprotein of N-terminal FLAG tagged mLangerin ECD was loaded in serial,two-fold dilutions (FIG. 2A). The serially diluted samples were blottedin 1 μg/ml of anti-FLAG mouse IgG mAb M2 or rat IgG mAb L5, followed bydetection with secondary anti-mouse IgG or anti-rat IgG antibodiesrespectively. The results with the two anti-FLAG mAbs indicated that mAbL5 could detect the FLAG tagged protein at 4 fold lower amounts than M2mAb (FIG. 2A). The inventors also performed Western blot analyses withFLAG-mSIGN-R1.ECD, another N-terminal FLAG tagged recombinant protein.The cell lysate of 293T cells transfected with FLAG-mSIGN-R1.ECDconstruct was analyzed in serial, two-fold dilution with mAbs M2 and L5as above. Similar to the results from purified, N-terminal FLAG taggedprotein, mAb L5 could detect anti-FLAG signals in the cell lysates with8 fold fewer cells (FIG. 2B). To test whether the location of FLAGepitope tag could affect the binding sensitivity, a rP11-FLAG.HAconstruct was made, in which the FLAG epitope was inserted at theC-terminus of rat p11 ORF (FIG. 2C), and transfected into 293T cells.Again in this C-terminal FLAG tagged recombinant protein, mAb L5 coulddetect FLAG in cell lysates from as little as 1250 cells, whereas thedetection of mAb M2 required cell lysates from 2500 cells (FIG. 2C).Therefore, mAb L5 detects both N-terminal and C-terminal FLAG taggedproteins 2-8 times better than the conventional anti-FLAG mAb M2.

Example 3 Mapping of the Epitope Detected by mAb L2, Renamed OLLA-2

As shown in FIG. 1, mAb L2 recognized an undefined epitope inOFL-mLangerin ECD, indicating the C-terminal half of OFL was required tobe detected by mAb L2. To map the epitope recognized by OLLA-2, theinventors designed serial deleted constructs. First, mLangerin ECD wasfused with human CD8 ECD with OFL, and serial deletions were made fromthe C-terminus (FIG. 3A). 293T cells were transfected with eachconstruct, lysed, followed by the Western blotting with anti-hCD8 (FIG.3B, left panel) and mAb L2 (FIG. 3B, right panel). The results showedthat the epitope of mAb L2 included the N-terminal region of themLangerin ECD (FIG. 3B, right panel, lanes 2 & 3). Subsequently, the 14amino acid peptide epitope recognized by mAb L2 as SGFANELGPRLMGK (SEQID NO: 1, FIG. 3C) was defined and named the tag, OLLAS (E. coli OmpFLinker and mouse Langerin fusion Sequence). The inventors also renamedmAb L2 as mAb OLLA-2. Notably, the construct comprising the fragment ofOLLAS lacking three amino acids at C-terminus of SEQ ID NO: 1 did notbind mAb OLLA-2 as well as the construct having these three amino acids(compare lns 2 and 3 in the right panel of FIG. 3B).

Example 4 The Use of OLLAS Epitope as a Tag for Immunodetection andImmunoprecipitation of Recombinant EGFP Proteins

To confirm the use of the new OLLAS epitope as a tag to detect fusionproteins, the OLLAS sequence (SGFANELGPRLMGK, SEQ ID NO: 1) to theN-terminus, the C-terminus, and internal sites of recombinant EGFPproteins was fused (FIG. 4A). The expression vectors for theserecombinant EGFP proteins were transfected into 293T cells. The celllysates were subjected to SDS-PAGE followed by Western blot detectionwith anti-GFP and mAb OLLA-2 (FIG. 4B, left panels). Then, these celllysates were subjected to immunoprecipitation with mAb OLLA-2 followedby the Western blot detection of the immunoprecipitates with anti-GFPand mAb OLLA-2 (FIG. 4B, right panels). Detection by anti-GFP or mAbOLLA-2 was clearly visible by Western blot analyses of the cell lysatesregardless of the location of the OLLAS epitope (FIG. 4B, left panels).Detection of the immunoprecipitates by anti-GFP indicated thatsuccessful immunoprecipitation was also achieved with OLLAS epitopetagged proteins by mAb OLLA-2 (FIG. 4B, right panels). In addition, theexpression vectors for EGFP alone and OLLAS tagged EGFP were transfectedinto CHO cells to test immunofluorescent staining of cells with mAbOLLA-2. Only the OLLAS epitope tagged EGFP was co-stained with mAbOLLA-2 (FIG. 4C, lower panels), indicating that the OLLAS epitope issuitable for the fluorescent immunocytochemistry. These data demonstratethat OLLAS is a superior tag for immunodetection of OLLAS-taggedproteins.

Example 5 Comparison of Binding Sensitivity of mAb OLLA-2 and OtherAnti-Epitope Tag mAbs by Western Blot Analyses

To compare the binding sensitivity of anti-OLLAS tag mAb OLLA-2 withanti-FLAG tag mAbs M2 and L5, EGFP protein was fused with FLAG and OLLAStag in tandem at the N-terminus (FIG. 5A). 293T cells were transfectedwith this FLAG.OLLAS-EGFP expression vector, lysed, and analyzed inserial, two-fold dilutions by Western blotting with 0.5 μg/ml ofanti-FLAG mAbs M2 and L5 as well as mAb OLLA-2 (FIG. 5A). The resultshows that mAb OLLA-2 binds to its OLLAS epitope with at least 100-foldmore sensitivity than anti-FLAG mAb M2 and with at least 30-fold moresensitivity than anti-FLAG mAb L5.

Next, to compare the binding sensitivity of mAb OLLA-2 with anti-V5 mAb(Invitrogen catalog number R960), human IgG1 Fc protein was fused withV5 epitope at the N-terminus and with OLLAS epitope at the C-terminus(FIG. 5B). 293T cells were transfected with this V5-hIgG1Fc-OLLASexpression vector, lysed, and analyzed in serial, two-fold dilutions forthe Western blotting with 1 μg/ml of anti-V5 mAb and mAb OLLA-2 (FIG.5B). The results showed that mAb OLLA-2 bound to its OLLAS epitope withat least 100-fold more sensitivity than anti-V5 mAb. These findingsindicate that the OLLA-2 mAb possesses very strong affinity for theOLLAS epitope, i.e. SGFANELGPRLMGK (SEQ ID NO: 1), and reactsspecifically with recombinant proteins containing this epitope.

Example 6 OLLAS Epitope is a Suitable Tag on Engineered mAb forImmunodetection

To test whether the OLLAS epitope was suitable as a tag for engineeredmAbs, the sequence was fused to the C-terminus of the heavy chain ofmurinized NLDC145 (mNLDC145; FIG. 6A), a cloned and engineeredanti-mouse DEC205 mAb (Hawiger et al., 2001). The culture supernatantsfrom 293T cells, which had been transiently transfected with mNLDC145 ormNLDC145.OLLAS expression vectors, were collected and separated inSDS-PAGE gels followed by Western blotting with anti-mouse IgG (FIG. 6B,upper panel) and mAb OLLA-2 (FIG. 6B, lower panel). The OLLA-2 mAb wasspecific for the engineered mNLDC145.OLLAS mAb.

To confirm the usage of OLLAS epitope as a tag for engineered mAbs, theculture supernatants from 293T cells transfected with mNLDC145 ormNLDC145.OLLAS expression vectors were used for FACS analysis. StableCHO cells expressing mDEC205 (CHO/mDEC205 cells) were incubated witheach supernatant and stained with mAb OLLA-2 followed PE-conjugatedanti-rat IgG prior to flow cytometry (FIG. 7A). The result showed thatonly mNLDC145.OLLAS with mAb OLLA-2 was able to stain the CHO/mDEC205cells. For fluorescent immunocytochemistry, CHO/mDEC205 cells wereincubated with the culture supernatants containing mNLDC145 ormNLDC145.OLLAS (FIG. 7B). Then, cells were stained with anti-mouse IgGand mAb OLLA-2 with anti-rat IgG. The result showed that the OLLA-2signal co-localized with anti-mouse IgG, i.e. mNLDC145, signal only whenmNLDC145.OLLAS supernatant was used (FIG. 7B, right panel).

For fluorescent immunohistochemistry, mouse lymph nodes were incubatedwith rat IgG control, rat IgG mAb NLDC145, or engineered mNLDC145.OLLASrespectively. Subsequently, all lymph nodes were further stained withmAb OLLA-2 and anti-rat IgG labeled with Alexa488 and anti-B220. Theseresults showed that mAb OLLA-2 was specific and sensitive to the OLLASepitope and that there was no non-specific, background signals in thetissue staining of lymph nodes. These findings confirm that the OLLASepitope and mAb OLLA-2 is broadly useful in various immunodetectionmethods, including FACS analysis and fluorescent immunostaining.

Example 7 Improved Immunodetection with OLLAS Epitope Tag

As shown in FIG. 7C, murinized mAb mNLDC145.OLLAS was able to detectmDEC205 in sections of lymph node tissues (FIG. 7C, lower panels),whereas rat IgG mAb NLDC145 was not sensitive enough (FIG. 7C, middlepanels). This might be explained because the detection of mNLDC145.OLLASrequired the secondary mAb OLLA-2 followed by the fluorescent labeledtertiary anti-rat IgG Ab, while the detection of NLDC145 required onlythe fluorescent labeled anti-rat IgG Ab.

In order to compare directly the use of mNLDC145.OLLAS and mAb OLLA-2,two engineered mAbs with the OLLAS epitope tag were generated (FIG. 8A).Expression vectors for murinized isotype control mAb fused with OLLASepitope and ovalbumin (mIsotype.OLLAS.OVA) and mAb mNLDC145 fused withOLLAS epitope and ovalbumin (mNLDC145.OLLAS.OVA) were transfected into293T cells. Then, mIsotype.OLLAS.OVA and mNLDC145.OLLAS.OVA mAbs werepurified from culture supernatants. MAb OLLA-2 were also purified andthen labeled with Alexa647 fluorochrome. As shown in FIG. 8B, under thesame conditions, CHO/mDEC205 cells incubated with mNLDC145.OLLAS.OVAwere better detected by Alexa647 labeled OLLA-2 than Alexa647 labeledanti-mouse IgG.

Then, the inventors examined the lymph node tissues stained with eitherengineered mAb mNLDC145.OLLAS.OVA or rat mAb NLDC145 followed byvisualization with Alexa647 labeled OLLA-2 and Alexa647 labeled anti-ratIgG, respectively (FIG. 8C). Unlike the previous result of lymph modesstaining by mAb NLDC145 with Alexa488 labeled anti-rat IgG (FIG. 7C,middle panels), mAb NLDC145 with Alexa647 labeled anti-rat IgG was ableto detect mDEC205 in sections of lymph node tissues (FIG. 8C, leftpanel) as efficiently as mAb mNLDC145.OLLAS.OVA with Alexa647 labeledOLLA-2 (FIG. 8C, right panel). These results demonstrate that OLLASepitope is a useful tag for engineered mAbs, which then can be usedbetter than or as efficiently as original mAbs in various applicationsof immunodetection. It was also found that the use of OLLAS peptide asan inter-molecular linker between two recombinant proteins, such as inmNLDC145.OLLAS.OVA and mIsotype.OLLAS.OVA, improved the expression ofrecombinant fusion proteins (data not shown) without losing its role asa highly effective epitope tag in various immunodetections.

Example 8 Analysis of Secondary Structures of OFL and OLLAs Sequences

A secondary structure prediction program called PSIPRED (Bryson et al.,2005; McGuffin et al., 2000) was utilized to characterize possibleconformations of the OFL and OLLAS sequences used in-between the fusedproteins that were generated successfully in previous (Galustian et al.,Int Immunol. 16(6):853-866 (2004)) and current studies. As shown in FIG.9, 20 amino acids before and after the OFL and OLLAS linkers wereincluded into the query sequences to increase the accuracy of thepredicted secondary structures. The OFL linker mostly adopts a randomcoil conformation, while the OLLAS linker shows a strong propensity toform an α-helical conformation.

In a non limiting way, the instant invention may be summarized asfollows.

Monoclonal antibodies against epitope tags are an efficient, convenientand rapid method for detecting recombinant protein expression (Jarvikand Telmer, 1998). If there is no antibody against the protein ofinterest, adding an epitope tag to this protein allows for proteindetection with an antibody against the epitope sequence. For example,affinity tags such as a FLAG-tag appended to recombinant proteins havetraditionally been used as a way of purifying proteins using standardconditions rather than developing individual biochemical purificationsbased on each protein's physical characteristics (Hopp et al., 1988).

Previously, rats were immunized to produce anti-mLangerin/CD207 antibodyusing two different forms of fusion proteins for mLangerin ECD expressedand purified from culture supernatants of stably transfected CHO cells(Cheong et al., 2007). As fusion partners of mLangerin ECD, FLAG epitopeand flexible linker sequences from E. coli OmpF protein (OFL) were used.FLAG epitope was chosen for column purification and OFL was chosen tofacilitate the folding of fusion proteins and to increase secretion fromthe cells. The OFL sequence as a linker was initially employed becausethe OFL sequence was viewed as highly flexible based on the moleculardynamics simulation of OmpF from E. coli (Im and Roux, J Mol Biol.319(5):1177-1197 (2002)). Although the OFL sequence forms a beta-hairpinloop in OmpF, the secondary prediction by PSIPRED (Bryson et al., 2005;McGuffin et al., 2000) indicates that the OFL exists as a flexible coilin-between the fused proteins. This prediction is corroborated by thesuccessful expressions of fusion proteins for C-type lectins, which werefunctional in sugar binding activities (Galustian et al., 2004) as wellas immunogenic in mAb productions (Kang et al., 2004; Cheong et al.,2007).

In the process, it was found that new mAbs L5 and OLLA-2 were specificto the FLAG/OFL tagged mLangerin ECD protein, not to mLangerin ECD.Applicants demonstrate that L5 is a new anti-FLAG mAb (FIG. 1) andOLLA-2 is a highly reactive mAb against a new epitope tag (FIGS. 1 and3). The new anti-FLAG L5 mAb shows high sensitivity for the FLAG epitopeand specificity for both N-terminally and C-terminally tagged FLAGepitope. In Western blot analyses, L5 can detect as little as 25 ng ofN-terminally FLAG tagged purified protein (FIG. 2A) and lysates from2,500 cells transfected with N-terminally FLAG tagged recombinantprotein construct (FIG. 2B). Conventional anti-FLAG M2 can detect 100 ngof N-terminally FLAG tagged purified protein (FIG. 2A) and lysates from20,000 cells transfected with N-terminally FLAG tagged recombinantprotein construct (FIG. 2B). Besides highly enhanced reactivity againstthe FLAG epitope, the new anti-FLAG L5 is a rat IgG mAb and provides anadditional option in immunostaining since all other conventionalanti-FLAG antibodies are mouse monoclonals or rabbit polyclonals.

MAb L2 or OLLA-2 is a novel rat IgG mAb against the newly identifiedepitope (SGFANELGPRLMGK, SEQ ID NO: 1) named OLLAS, with many advantagesin recombinant protein engineering and immunodetection. First, thisnovel pair of tag and anti-tag mAb has a remarkable sensitivity and thusenhances the performance of a variety of immunodetection methods,including Western blot, immunocytochemistry, immunohistochemistry, flowcytometry, and immunoprecipitation. Especially, mAb OLLA-2 can detectthe OLLAS epitope tagged proteins by Western blotting with more than 100fold higher sensitivity than anti-FLAG M2 and anti-V5 mAbs. Second, thenew OLLAS epitope can be fused to the C-terminal, the N-terminal, andthe internal (or linker) sites of recombinant and fusion proteinsincluding the engineered mAbs. The OLLAS epitope does not interfere withthe biological activities of the recombinant proteins where it wasinserted, such as fluorescence of EGFP and binding of antibodies, andcan improve the expression of recombinant proteins as an inter-molecularlinker between two recombinant proteins, as shown in the engineering ofanti-mDEC205 mAb fused with ovalbumin. Third, mAb OLLA-2, as a rat IgG,can be used for the immunostaining of mouse and human samples withoutdirect labelling of fluorochrome or enzyme. Because anti-tag mAbs andAbs are mostly made from mouse and rabbit, the anti-OLLAS tag mAb OLLA-2from rat IgG will provide an extra advantage in immunodetection.

As indicated in FIG. 3C, the OFL sequence contains two N-glycosylationsites. It is possible that the N-glycosylation in OFL region couldinterfere with the structural integrity of the fusion proteins and/orthe antibody responses against the fusion proteins where the OFL linkerwas used. However, the newly identified OLLAS epitope sequence does nothave any N-glycosylation site. Unlike OFL, when the OLLAS are used as alinker in the fused proteins, it is predicted to adapt an alpha-helicalconformation by PSIPRED (FIG. 9). It has been suggested that, in linkerengineering, the helical linkers like OLLAS are better than flexiblelinkers like OFL to maximize the desired function of engineered fusionproteins (Arai et al., Protein Eng. 14(8): 529-532 (2001)). Asdemonstrated in FIG. 8, the OLLAS sequence appears to function properlyas a linker in the engineered mAbs fused with antigens. In addition, theOLLAS sequence is a superior protein-tagging epitope to other currentlyexisting tag epitopes. It should be stressed that the OLLAS, generatedby fusion between the sequences from E. coli and mouse, is a syntheticsequence different from any of the known protein sequences in nature,indicated by the NCBI BLAST search. The uniqueness of its sequence maymake the OLLAS tag more useful for many different applications inimmunodetection, especially in vivo applications in diverse organisms.

Thus, the present invention provides that mAb L5 is a new anti-FLAG withhigher sensitivity, and that the novel OLLAS epitope and mAb OLLA-2 aresuperior tag and anti-tag mAb in terms of highly sensitive detection,broader range of applications, sequence uniqueness, and potential use asa linker. These new epitope tag and anti-tag mAbs will improve thecurrent immunodetection methods for recombinant proteins.

All publications cited in the specification, both patent publicationsand non-patent publications, are indicative of the level of skill ofthose skilled in the art to which this invention pertains. All thesepublications are herein fully incorporated by reference to the sameextent as if each individual publication were specifically andindividually indicated as being incorporated by reference.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. An isolated antibody or an antigen-bindingportion thereof which selectively binds to a polypeptide comprising thesequence of SEQ ID NO: 1 or a fragment thereof selected from the groupconsisting of SEQ ID NO: 4-SEQ ID NO:
 17. 2. The antibody of claim 1,wherein the antibody is a rat IgG monoclonal antibody (mAb).
 3. A kitcomprising: a) a first antibody of claim 1 and b) a detection reagentsuitable for detecting the first antibody; and c) a set of instructions.4. The kit of claim 3, wherein the first antibody selectively binds to apolypeptide comprising the sequence of SEQ ID NO:
 1. 5. The kit of claim3 wherein the detection reagent comprises a secondary antibody.
 6. Thekit of claim 5, wherein the secondary antibody selectively binds to thefirst antibody.
 7. The kit of claim 5, wherein the secondary antibody islabeled with a reporter molecule.
 8. The kit of claim 7, wherein thereporter molecule is one selected from the group consisting of anenzyme, a fluorescent compound, a radioisotope, a chemiluminescent, anda bioluminescent molecule.
 9. The kit of claim 8, wherein the enzyme isone selected from the group consisting of horseradish peroxidase,glucose oxidase, beta-galactosidase and alkaline phosphatase.
 10. Thekit of claim 8, wherein the fluorescent compound is fluorescein orrhodamine.
 11. The kit of claim 3 further comprising a reportermolecule.
 12. The kit of claim 3, wherein the first antibody is bound toa solid support.
 13. The kit of claim 3, further comprising one or moreselected from the group consisting of a cloning vector, a forwardprimer, a reverse primer, a ligase, a restriction endonuclease,competent cells, and a control.
 14. The kit of claim 13, wherein thecontrol is a vector comprising a DNA sequence that encodes anOLLAS-tagged protein.
 15. The kit of claim 14, wherein the kit furthercomprises a second antibody that selectively binds to the OLLAS-taggedprotein.
 16. The kit of claim 15, wherein the second antibody is labeledwith a reporter molecule.
 17. The kit of claim 16, wherein the reportermolecule is one selected from the group consisting of an enzyme, afluorescent compound, a radioisotope, a chemiluminescent, and abioluminescent molecule.
 18. The antibody of claim 1, wherein theantibody is a monoclonal antibody.
 19. The antibody of claim 1, whereinthe antibody is a chimeric antibody.
 20. The antibody of claim 1,wherein the antibody is a humanized antibody.